1. Field of the Invention
The field of art to which this invention pertains is hydrocarbon processing. Specifically this invention relates to a fluid catalytic cracking process for simultaneously cracking a gas oil feed and upgrading a gasoline-range feed to produce high quality motor fuel.
2. Prior Art
For years poor quality or hard to process gasoline-range streams such as coker, visbreaker, or pyrolysis naphtha have been charged to FCC units (or to gas concentration processes located downstream of FCC units) for the purpose of merely disposing of them rather than upgrading such materials. These materials when charged to the FCC process entered the process with the normal gas oil feed and were essentially converted to coke on catalyst in the relatively long residence time, dense bed reacton zones which were employed at the time. Alternatively, some of these gasoline-range materials passed through the reaction zone with little or no change in quality or composition.
The advent of higher activity catalysts and the use of short-time dilute-phase riser reaction zones has made it possible not only to more efficiently crack gas oil feed streams but possible to upgrade in the FCC process most of these gasoline-range materials into more valuable products rather than merely disposing of them. By separately contacting the gasoline-range feed and the gas oil feed with catalyst in different regions of a short-time riser reaction zone which are maintained at different cracking conditions a high quality high octane motor fuel can be produced. Since the refiner now has a method whereby he can economically upgrade low value gasoline-range streams the process of this invention is a profitable operation for the refiner. Upgrading of such gasoline streams, including the more refractory materials such as straight run gasoline, can be more efficiently achieved when the temperature of the freshly regenerated catalyst which contacts such feeds is increased. In one embodiment of the process of our invention the temperature of the regenerated catalyst is increased by employing a regeneration zone in which CO, resulting from the combustion of coke, is essentially completely combusted to CO.sub.2 and in which heat of combustion of the CO is transferred to the regenerated catalyst.
The prior art has recognized that hydrogenation of these low octane, generally unstable gasoline-range streams improves their ability to be catalytically cracked. In U.S. Pat. No. 3,065,166 for instance, a heavy gasoline fraction (boiling range of about 350.degree.-425.degree. F.) is hydrogenated and contacted with hot regenerated catalyst from about 0.5 to 5 seconds in a separate reaction zone, distinct from the dense bed conversion zone wherein the FCC feed is cracked, for the purpose of reducing gas and coke formation and increasing the yield of 350.degree. F. end point gasoline.
In the process of our invention the gasoline-range (having a boiling range of from about 100.degree. F. to about 430.degree. F.) feed without prior hydrogenation is contacted with freshly regenerated catalyst in a particular region of a short-time dilute-phase riser reaction zone for less than about 0.5 seconds for the purpose of upgrading the gasoline-range feed to produce stable high octane motor fuel. Additionally some amounts of coke and gas are produced so overall yields of the products from the reaction zone are somewhat increased rather than decreased. The normal FCC gas oil feed then enters the same reaction zone but in a different region.
In U.S. Pat. No. 3,617,497gasoline yield is enhanced by segregating normal FCC gas oil feed into a relatively low molecular weight gas oil feed stream and a relatively high molecular weight gas oil feed stream and charging the lower molecular weight fraction near the bottom of a transfer line reactor and the relatively higher molecular weight fraction progressively further up to the riser both in the presence of an added diluent vapor which reduces the partial pressure of the lower molecular weight fraction. No mention is made of upgrading a gasoline-range hydrocarbon feed. A gasoline-range hydrocarbon, if used at all, will be used as a diluent.
The prior art has neither recognized nor suggested the process of our invention.